[circuit10]

Wouldn’t that degrade the quality for a lossy format, especially if done repeatedly? I see why people would not want their phone to do that. If you’re uploading it somewhere that might not be supported it would be worth it but I don’t want my phone to silently degrade images that are just sitting in my gallery

[coldpie]

Rotate it at capture time, before encoding. This would get rid of like 95% of these exif orientation tags. For images that need to be manually rotated after for whatever reason, sure I guess you have a point, though I'd argue the quality loss would be unnoticeable in practice unless you're like spinning the image in circles 100 times for some reason.

[justincormack]

JPEG allows for lossless 90 degree rotation, not sure about other formats

[derefr]

Pretty sure that any software from after ~2005 that supports image rotation, isn’t doing so at decoding time, but rather is decoding the image into a GPU texture buffer and then rotating the quad that texture gets applied to. Which should always be lossless for multiple-of-90-degree rotations. (Presuming that the image doesn’t depend on sub-pixel rendering tricks.)

[ryandrake]

Even without a GPU, the JPEG format itself allows for totally lossless rotation. It is also quite fast, and doesn't require reading and writing every pixel in the image.

[thunderfork]

Isn't this only true for images where the resolution is divisible by the block size or something like that?

IIRC in other cases you have to cut the edge of the image off (rounded to the nearest block) or recompress those edge blocks

[drewnoakes]

Is that still true if the image dimensions aren't a multiple of the block size?